1. Field of the Invention
The present invention relates to a method for temporarily sealing the open ends of a plurality of fluid transport conduits that terminate in a common header space. In particular, the invention relates to a method for simultaneously sealing off the ends of heat exchanger tubes at their junction with a common header space to permit, for example, identification of a leaking tube by conventional vacuum testing techniques.
2. Background of the Invention
In apparatus of the general type having a number of elongated fluid transport means arranged with open first ends terminating in a common header space, such as a heat exchanger, a leak may develop in one of the conduits which will allow fluid on one side of the conduits to contaminate fluid on the other side. It then becomes necessary to identify which tube is leaking, so that it may be quickly replaced or repaired.
The usual procedure for determining which is the leaking tube involves temporarily closing off one end of each of the tubes individually with a rubber seal, a blank flange, or an equivalent device for providing a vacuum-tight seal. A detection device and a vacuum pump or other vacuum source are then connected to the other end of each of the conduits in turn, while the exterior of the conduits is surrounded with a detectable gas. If the conduit is sound, no gas will penetrate to the interior, and the detection device will not indicate. On the other hand, if there is any leak in the wall of the conduit, the gas will be sucked through the leak into the interior of the conduit and will actuate the detection device, thus identifying the defective conduit.
Although the conventional method of sealing each conduit end individually is satisfactory for apparatus in which there are relatively few conduits and the ends are easily accessible, this procedure becomes time consuming and difficult if the apparatus contains a large number of conduits, or if partial disassembly is required to gain access to the conduit openings in the header space.
In particular, this procedure presents severe problems in the case of a heat exchanger for generating steam in a sodium-cooled nuclear reactor plant. A typical steam generator for such a plant may comprise a heat exchanger having as many as 70 tubes of small internal diameter (e.g., 20 mm). The tubes extend through a sodium compartment, with one end of each tube terminating in a common feedwater header and the other terminating in a common steam header. Liquid sodium, heated in the reactor, circulates through the sodium compartment and transfers its heat through the tube walls to water flowing from the feedwater header into the tubes. The heated water emerges as steam from the other ends of the tubes into the steam header; from there it may flow to a steam turbine.
Proper and safe operation of the nuclear plant demands that any leak which may occur in the heat exchanger tubes be corrected as soon as possible to prevent any significant contact between the water or steam inside the tubes and the liquid sodium outside the tubes in the sodium compartment. Thus, when a leak occurs it is desirable to identify the faulty tube as quickly as possible; so that it can be replaced, repaired, or permanently sealed off. Because of the relatively large number of tubes and because the tubes are not readily accessible through the feedwater header, the conventional procedure of individually closing off the tube ends with rubber plugs or blind flanges is time consuming and expensive.